Conventional integral ink jet cartridges and exchangeable ink jet cartridges of ink jet printers require a complicated valve system in order to prevent ink leaks from the pressure release valve open to the atmosphere in the case of the former cartridges or from the joint of the ink tank and the ink jet head in the case of the latter cartridges. Hence, it has been proposed to provide an ink holding member in an ink tank so as to avoid the above-mentioned problems of conventional ink tanks.
Ink holding members which have hitherto been proposed for use in the inside of an ink tank include the foamed material disclosed in JP-A-63-87242 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), the member capable of retaining liquid disclosed in JP-A-2-514, the porous member disclosed in JP-A-2-34353 and JP-A-3-87266, the ink absorbing member disclosed in JP-A-3-136854, and the porous or fibrous material disclosed in JP-A-3-136861. A kind of polyurethane sponge is known as a material of these ink holding members.
In the production of the conventional ink holding member, foamed materials, such as polyurethane foam, easily provide a porous structure having uniform porosity and have excellent ink holding ability for some kinds of inks. However, the foamed material is unsatisfactory as a means for efficiently furnishing ink to nozzles through which the ink is spouted. That is, the foamed material should be provided with a density gradient by, for example, mechanical compression so as to have such a shape that ink is easily transferred. Further, in cases where an ink holding member made of such a porous material has low wettability, ink filling at the time of shipping from factories is a time-consuming operation.
In order to solve the above-described problems, it has been proposed to use general fibrous materials as ink holding material. A fibrous material can be provided with a density gradient so as to give excellent ink transfer properties by an easy operation of changing the fiber density when it is put in an ink tank. In addition, since a fibrous material can have a high porocity, it is easy to fill the fibrous ink holding member with ink even if the material has poor wettability.
However, a fibrous material must be cut to an appropriate size before it is put in an ink tank. It follows that the fiber dust generated on cutting runs with ink and reaches the recording head, resulting in deterioration of ink jet properties. Means which have been taken against this problem include a filter, etc. which is provided between an ink tank and a recording head to inhibit the fiber dust from reaching the recording head. In addition to the above problem, natural fibers are associated with the disadvantage that various impurities inherent to natural fibers, such as fats and oils, run with ink or react with each other, resulting in deterioration of ink characteristics or ink jet properties. On the other hand, chemical fibers contain various additives added during the preparation, such as antistatic agents, smoothing agents, and emulsifying agents, affect the ink to cause deterioration of ink characteristics or ink jet properties.
Accordingly, the present invention has been completed in the light of the above-mentioned problems of conventional techniques.